However, he believes the current system of self-regulation is "reaching its outer limits".

He told BBC Radio Five Live that "unless the industry can show pretty quickly that they're at or close to 100% coverage in Britain, I'm afraid we will be going to talk to our MPs... demanding legislation".

He said that as BT estimated it had one-third of the market, to extrapolate across the whole domestic internet market would mean there were 100,000 hits per day or 4 million per year.

Proven technology

According to the industry about 80% of domestic internet users in the UK are covered by BT Cleanfeed-type solutions, he said, but he also raised concerns that there was "some scepticism" about that figure and called for it to be independently verified.

"Even if it's true, it means that one in five domestic internet users could access these illegal sites without any obstacles at all.

"That is not acceptable. It needs to be 100%.

"BT has proven that the technology works so there really isn't any excuse for any internet service provider not doing it," Mr Carr added.